Beam scanning lithography is a well-known field, see for instance Allen, U.S. Pat. No. 5,255,051 and Allen et al., U.S. Pat. Nos. 5,327,338 and 5,386,221, describing systems which use an array of light beams (typically laser beams) and an optical system involving reflective optics for imaging a pattern onto a substrate. A typical application is for generating patterns for use in semiconductor lithography. The array of light beams is scanned across a substrate in a controlled fashion with the beams being turned on and off in order to expose a photosensitive resist on a surface of the substrate. The exposed areas are then developed, defining a pattern in the resist which is later used for other steps such as etching, etc. Such lithography machines typically use an array of laser beams often referred to as a "brush" with a number of very small diameter laser beams arranged in a line or an m.times.n array where m and n are integers each greater than or equal to one.
Typically the light beams are independently modulated, that is turned on or off or modulated between being on and off and so having a gray scale level of intensity. There are also known systems using light beams in which the light beams, instead of being incident on a semiconductor wafer, are incident on a semiconductor which is a photocathode. The incident light beams generate electrons ejected from the photocathode which in turn form an electron beam which in turn is used to define a pattern on, for instance, a sensitive substrate.
It is well known to provide a linear array of laser beams from a single laser; see Allen, U.S. Pat. No. 4,797,696, incorporated herein by reference in its entirety. For many types of pattern generating systems, rather than a single linear array of beams it is desirable to have a rectangular m.times.n array. This array is called rectangular because the beams are arranged in a shape which is rectangular in a plane perpendicular to the axis of the beams. Each individual beam in cross-section is typically circular, although this is of no particular importance to this disclosure.
It would be desirable therefore to find a simple and efficient (lossless) way to transform such an initial linear array of equal intensity light beams, for instance laser beams, into a rectangular shaped array of equal intensity beams. It is important that the transformation be essentially lossless so that the full intensity of each individual beam is preserved but it is moved, in terms of location, relative to other of the beams. It is also important that the pitch (the spacing between beam centers) be precise for accurate lithography.